Many people have questioned Depp's ongoing involvement as Gellert Grindelwald in the Harry Potter prequels after his former wife Amber Heard alleged he had been physically and mentally abusive to her throughout their short-lived marriage.

The 31-year-old actress obtained a temporary restraining order when she first split from Depp in 2016.

Harry Potter author J.K. Rowling previously defended the decision to keep Depp in the films, but Radcliffe, who played the boy wizard, isn't sure the producers made the right decision.

"It's a very hard thing for me," he tells Entertainment Weekly, explaining he wants to be supportive of the producers behind his Harry Potter films. "I can see why people are frustrated."

Radcliffe adds, "I'm not saying anything that anybody hasn't already said - and this is a weird analogy to draw - (but) in the NFL (National Football League), there are lots of players arrested for smoking weed and there is other people's behaviour that goes way beyond that (sic), and it's tolerated because they're very famous players.

"I suppose the thing I was struck by was, we did have a guy (Jamie Waylett) who was reprimanded for weed on the (original Potter) film, essentially, so obviously what Johnny has been accused of is much greater than that."

Waylett starred in six franchise films, but was dropped from Harry Potter and the Deathly Hallows after he was arrested for growing marijuana plants. He subsequently pleaded guilty and was sentenced to community service.

Meanwhile, Johnny will star in the next Fantastic Beasts movie, The Crimes of Grindelwald, alongside Eddie Redmayne, Katherine Waterston, Jude Law, and Ezra Miller. The film hits theatres in November (18).